<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      * {
        margin: 0;
      }
      .flex-box {
        width: 500px;
        margin: 0 auto;
        display: flex;
        border: 2px dashed #fac;
      }
      .flex-item {
        width: 100px;
        height: 100px;
        color: #fff;
        font-size: 32px;
        text-align: center;
        line-height: 100px;
      }
      .flex-item:nth-of-type(1) {
        background-color: #fca;
      }
      .flex-item:nth-of-type(2) {
        background-color: #fac;
      }
      .flex-item:nth-of-type(3) {
        background-color: #acf;
      }
      .flex-item:nth-of-type(4) {
        background-color: #afc;
      }
      .flex-item:nth-of-type(5) {
        background-color: #caf;
      }
      .flex-item:nth-of-type(6) {
        background-color: #cfa;
      }
    </style>
  </head>
  <body>
    <div class="flex-box">
      <div class="flex-item">1</div>
      <div class="flex-item">2</div>
      <div class="flex-item">3</div>
    </div>
    <!-- 
      1 1 1
      3

      1/3
      1/3
      1/3
     -->
  </body>
</html>

